In various locations along Japan's coast, TV footage showed massive damage from the tsunami, with dozens of cars, boats and even buildings being carried along by waters. A large ship swept away by the tsunami rammed directly into a breakwater in Kesennuma city in Miyagi prefecture, according to footage on public broadcaster NHK.
Officials were trying to assess damage, injuries and deaths from the quake but had no immediate details.
The quake that struck at 2:46 p.m. was followed by a series of powerful aftershocks, including a 7.4-magnitude one about 30 minutes later. The U.S. Geological Survey upgraded the strength of the first quake to a magnitude 8.9, while Japan's meteorological agency measured it at 7.9.
The meteorological agency issued a tsunami warning for the entire Pacific coast of Japan. NHK was warning those near the coast to get to safer ground.
The Pacific Tsunami Warning Center in Hawaii said a tsunami warning was in effect for Japan, Russia, Marcus Island and the Northern Marianas. A tsunami watch has been issued for Guam, Taiwan, the Philippines, Indonesia and the U.S. state of Hawaii.
The quake struck at a depth of six miles (10 kilometers), about 80 miles (125 kilometers) off the eastern coast, the agency said. The area is 240 miles (380 kilometers) northeast of Tokyo.
In downtown Tokyo, large buildings shook violently and workers poured into the street for safety. TV footage showed a large building on fire and bellowing smoke in the Odaiba district of Tokyo.
In central Tokyo, trains were stopped and passengers walked along the tracks to platforms.
The ceiling in Kudan Kaikan, a large hall in Tokyo, collapsed, injuring an unknown number of people, NHK said.
Footage on NHK from their Sendai office showed employees stumbling around and books and papers crashing from desks. It also showed a glass shelter at a bus stop in Tokyo completely smashed by the quake and a weeping woman nearby being comforted by another woman.
Several quakes had hit the same region in recent days, including a 7.3 magnitude one on Wednesday.
Thirty minutes after the quake, tall buildings were still swaying in Tokyo and mobile phone networks were not working. Japan's Coast Guard has set up task force and officials are standing by for emergency contingencies, Coast Guard official Yosuke Oi said.
"I'm afraid we'll soon find out about damages, since the quake was so strong," he said